报告摘要：

In this talk, Nicolae C. Panoiu will review some of our recent results regarding nonlinear optical interactions in certain topological photonic systems, such as photonic crystals (PhCs) and graphene metasurfaces. In particular, he will present a detailed analysis of the band topology of 2D PhCs with hexagonal symmetry and demonstrate that nonlinear optical processes, such as second- and third-harmonic generation (SHG, THG) can be readily implemented via one-way edge modes of this setup. he also demonstrates that influence of the Kerr effect on valley-Hall topological transport in graphene metasurfaces can be used to implement an all-optical switch. To this end, by taking advantage of the large Kerr coefficient of graphene, the index of refraction of a topologically protected graphene metasurface can be tuned via a pump beam, which results in an optically controllable frequency shift of the photonic bands of the metasurface. This spectral shift can in turn be employed to control the propagation of an optical signal in certain domain-interface waveguide modes of the graphene metasurface. In the second part of my talk, he will illustrate how bound states in the continuum (BICs) of certain PhC slabs, engineered to possess sharp resonances with high quality factors at both the fundamental frequency (FF) and second-harmonic (SH) can be used to achieve an orders-of-magnitude enhancement of the SHG. Thus, he will first show that PhCs operating at telecommunication wavelengths support a pair of at-G resonances. This double-resonance phenomenon is subsequently used to significantly enhance the SHG from the PhC slabs. The existence of peaks in SHG spectra reveals the strong light-matter interaction facilitated by the double-resonance effect. The peak values of the SHG signal are several orders of magnitude larger than those corresponding to homogeneous slabs with the same thickness.

报告人简介：Biography:

Nicolae C. Panoiu is Professor of Nanophotonics in the Department of Electronic and Electrical Engineering, University College London. He received the B.Sc. and M.S. degrees in physics from the University of Bucharest, Bucharest, Romania, in 1990 and 1992, respectively, and the Ph.D. degree from New York University (USA), in 2001. After graduation he joined the Department of Applied Physics and Applied Mathematics at Columbia University (USA) as a Postdoctoral Fellow and later on as a Senior Research Scientist. While at Columbia University, he worked on the optical properties of nonlinear photonic crystals, plasmonic systems, metamaterials, and the theory of pulse propagation in silicon photonic nanowires. His current research interests include topological photonics, silicon photonics, optical properties of photonic nanostructures, classical and quantum metamaterials, and computational modeling of electromagnetic structures. He is the author or co-author of more than 250 research publications, including papers published in highly selective journals such as Nature Photonics, Nature Physics, Nature Communications, Sciences Advances, Physical Review Letters, Advanced Materials, and others.